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Horses Have a West Nile Vaccine; So Why Don't We?

By Brendan I. Koerner
Posted Wednesday, Aug. 14, 2002, at 1:34 PM ET

Tens of thousands of horses are being vaccinated against the West Nile virus. A human version of the vaccine likely won't be available for a decade, if ever. Why do horses have the pharmaceutical edge in the fight against West Nile?

Our animal friends are benefiting from the relative laxity of federal veterinary regulations. Last August, the U.S. Department of Agriculture gave conditional approval to an equine vaccine manufactured by Fort Dodge Animal Health, a division of Wyeth. Though the product's safety had been thoroughly proved, its efficacy against West Nile had not. But the USDA judged the virus to be a crisis, since horses are particularly susceptible—about a third of infected horses will perish, compared with around 10 percent of humans who exhibit symptoms. The agency thus exercised its right to grant an emergency OK for the vaccine's sale. About 2 million shots have been sold nationwide since then, at upward of $30 a pop.

The Food and Drug Administration is not similarly lenient when it comes to human vaccines, even for high-profile maladies like West Nile. Regardless of public paranoia, a vaccine's efficacy must be demonstrated over three phases of human clinical trials before earning the FDA's seal of approval. Researchers from the National Institute of Allergy and Infectious Diseases reported in March that they'd successfully vaccinated mice against the virus; they'll have to repeat their results in monkeys before moving on to clinical trials with humans. A private company called Acambis is a bit further along with its West Nile vaccine and hopes to begin human trials by year's end. But even perfect results won't get Acambis' shot into your doctor's offices before 2006 or 2007.

There's no need to envy the horses quite yet, as the jury's still out on how helpful Fort Dodge's vaccine really is long-term. But some zookeepers aren't waiting around for additional data. Burned by West Nile deaths among their exotic birds last year, several zoos are administering the equine vaccine to their avian populations. The Houston Zoo, for example, has vaccinated its flamingos and Attwater's prairie chickens.

Next question?

Explainer thanks Dr. Gregory Ferraro of the Center for Equine Health at the University of California-Davis and Dr. Patricia Repik of the National Institute of Allergy and Infectious Diseases.

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Brendan I. Koerner is a contributing editor at Wired and a columnist for Gizmodo. His first book, Now the Hell Will Start, is out now.
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